In Miami, a group of men live in a makeshift settlement under a bridge. They're not drifters or off-the-gridthey're convicted sex offenders.

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By 11 a.m., Juan Martin had given up on trying to sleep. It was October of last year, the morning after one of those rare Miami nights when the swelter gives way to balmy breezes. Even so, Martin had been unable to lose consciousness: Four feet above the cramped space he calls home, the concrete struts of the four-lane bridge that connects Miami Beach to the city 2 ½ miles west had registered every passing car. The night before, some of the other guys who live under the bridge had lit a bonfire on the sandy promontory that juts into the water, eventually turning in as the flames died down. But Martin had lain awake, his eyes fixed on the glittering skyline across the bay, wondering how it had all come to this. How could a handful of menmany with jobs, families, and homesfind themselves living under Miami-Dade County's Julia Tuttle Causeway?

As the drone of the morning traffic subsided, Martin, a 30-year-old Miami native with high cheekbones and a thin chin-strap goatee, rose from the two old chairs he'd pushed together to make a bed, brushed his teeth, and picked up a can of black spray paint. He used it to write just one word, which is still emblazonedin giant letterson the concrete embankment below the Julia Tuttle: why?

Ten months later, Martin is still under the bridge, and the number of men living with him has doubled. They have different backgrounds but one thing in common: They are all convicted sex offenders. Fourteen men, ranging in age from 30 to 83, call this place home. Some sleep in cars among the pilings, others in grimy Wal-Mart tents wedged beneath the bridge. Martin, who spent two years in jail after being convicted of exposing himself to a 16-year-old girl when he was 19 or 20 (a crime he says he didn't commit), no longer has to wear the black GPS monitoring device that many of his neighbors do. He finished his five-year probation in 2006, but he can't find a place to live that complies with the county's residency laws.

So Martin is forced to live herein a colony under an overpass where the amenities include a generator, a composting toilet, and a workout area with a bench and free weightsindefinitely, because he and the other men were ordered here by law-enforcement authorities.

"Take a picture if you want," says Martin, showing off his driver's license. The address next to his photo reads UNDER THE JULIA TUTTLE CAUSEWAY.

In the past, very few states required convicted sex offenders to register their home addresses. That changed in 1994, when, following the abduction of an 11-year-old Minnesota boy, Congress passed the Jacob Wetterling Crimes Against Children and Sexually Violent Offender Registration Act. The legislation gave states the option of establishing a registry or losing 10 percent of their criminal-justice funding (all chose the former). Florida, like many states, barred offenders from living within 1,000 feet of schools, parks, playgrounds, public-school-bus stops, or other places where children congregate. Then in 2005, when a 9-year-old girl named Jessica Lunsford was murdered by a 47-year-old drifter in Homosassa, Florida, communities across the state and country converted their outrage into more legislation. Miami Beach expanded its restricted areas to 2,500 feeteffectively banishing every offender in town. The situation escalated: County commissioners, nervously watching as the displaced spilled eastward into their districts, extended Miami Beach's local limits to the whole county. Other counties followed suit. There are now 128 local ordinances in Florida that limit where a sex offender can live. Critics say these laws are only making it harder for authorities to keep track of offenders. Some are just disappearingmeaning that they can show up in other towns, where no one knows their history, and face no monitoring from authorities. Since 2005, the number of absconders has tripled in Floridain Miami-Dade, the increase is tenfold. Nationwide, according to the National Center for Missing & Exploited Children, at least 100,000 sex offenders have become noncompliant. No one knows where they are.